This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A260299 #21 Feb 09 2021 01:57:12 %S A260299 1,2,4,15,17,22,23,27,28,31,34,43,46,47,54,56,61,63,67,73,75,76,83,91, %T A260299 92,95,96,101,107,109,111,115,117,120,129,132,141,143,144,146,149,150, %U A260299 153,154,155,164,167,181,190,192,193,205,208,214,215,219,224,225 %N A260299 Numbers k such that hyperfactorial(prime(k)-1) == 1 (mod prime(k)). %H A260299 Matthew Campbell and Charles R Greathouse IV, <a href="/A260299/b260299.txt">Table of n, a(n) for n = 1..10000</a> (first 2516 terms from Campbell) %F A260299 a(n) = pi(A260298(n)). %e A260299 The 4th prime is 7, and the hyperfactorial of 7 is 4031078400000, which is congruent to 1 mod 7. - _Kellen Myers_, Aug 19 2015 %t A260299 PrimePi[fQ[n_]:= Mod[Hyperfactorial[n - 1], n] == 1; Select[Prime@Range@250, fQ]] (* _Vincenzo Librandi_, Aug 20 2015 *) %o A260299 (PARI) is(n,p=prime(n))=prod(k=2,p-1,Mod(k,p)^k)==1 \\ _Charles R Greathouse IV_, Aug 29 2015 %Y A260299 Cf. A000040, A002109, A260178, A260297, A260298. %K A260299 nonn %O A260299 1,2 %A A260299 _Matthew Campbell_, Jul 22 2015